1. Field of the Invention
This invention relates generally to an improved diffusion monitoring apparatus, and more particularly, but not by way of limitation, to improved diffusion monitoring apparatus of the type including an evacuated hollow diffusion probe member connected to an evacuated collector chamber.
2. Description of the Prior Art
Apparatus for monitoring selected components of a fluid system whereby the selected components diffuse through a probe have heretofore been developed and used successfully. Generally, such monitoring apparatus include an evacuated elongated hollow probe member through which the components to be monitored diffuse, a closed evacuated collector chamber sealingly connected to the probe member and an ion pump means utilized as a collector chamber for providing an electrical current output in proportion to the rate of diffusion of the selected components. Such monitoring apparatus are especially useful in monitoring atomic hydrogen permeation of a steel probe exposed to a corrosive fluid, which hydrogen permeation indicates corrosion of the steel probe exposed to the fluid. The monitoring apparatus can be used to control the injection of inhibitor into the fluid system or to control other process variables so that corrosion in the system is maintained at a minimum.
In operation of such heretofore used diffusion monitoring apparatus, the probe member is formed of a selected material which allows the diffusion of one or more selected components from a fluid system. The probe member is connected to a collector chamber which is attached to an ion pump, and both the interior of the probe and the interior of the collector chamber are evacuated. While the probe can take a variety of configurations, it usually is comprised of an elongated hollow member closed at one end and sealingly connected to the collector chamber at the other end. The collector chamber includes a port communicating the interior of the chamber with the interior of the probe and an ion pump is contained in or connected to the other end of the chamber. The ion pump functions as a trap in which the selected components are ionized and accelerated by high electrical potential into an electrode where the component is buried or gettered, thus removing it from the collector chamber. As gases are trapped their presence is detected as a current differential exceeding a predetermined background value which can be read by a meter or utilized in a variety of control apparatus.
Heretofore, in order to evacuate the interior of the probe and collector chamber, the probe or collector chamber have been provided with a port connected to a shutoff valve (commonly referred to as a roughing valve) by conduit means. When starting up the monitoring apparatus, the shutoff valve is connected to a rough vacuum pump and the probe, collector chamber and ion pump evacuated thereby. After the evacuation has reached the point that the ion pump begins to operate the shutoff valve is closed and the rough vacuum pump disconnected therefrom. The use of such a shutoff valve with diffusion monitoring apparatus often constitutes a problem due to leakage of air through the valve into the probe and collector chamber brought about by wearout of the valve or the accidental opening of the valve thereby causing the vacuum to be lost and operation of the apparatus to be interrupted. Further, the use of such a shutoff valve adds to the overall cost of the apparatus.
By the present invention an improved diffusion monitoring apparatus is provided which obviates the requirement for a vacuum shutoff valve and the problems and expense attendant therewith as well as resulting in a smaller less bulky unit.